Numerous procedures involving catheters and other minimally invasive devices may be performed to provide a wide variety of medical treatments, such as ablation, angioplasty, dilation and others. The term “atrial fibrillation” is a type of cardiac arrhythmia, or irregular heartbeat, in which the atria fail to contract effectively. Normal sinus rhythm of the heart begins with an electrical impulse generated by the sinus node that propagates across the right and left atria (the two small upper chambers of the heart) to the atrioventricular node. Atrial contraction leads to pumping blood into the ventricles in synchronization with the electrical pulse.
During atrial fibrillation, disorganized electrical conduction in the atria causes rapid uncoordinated contractions, resulting in sub-optimal pumping of blood into the ventricle. The atrioventricular node may receive sporadic electrical impulses from many locations throughout the atria, instead of only from the sinus node. This electrical confusion may overwhelm the atrioventricular node, producing an irregular and rapid heartbeat. Consequently, blood may pool in the atria and increase a risk for blood clots.
While there are numerous variations of atrial fibrillation with different causes, they all involve irregularities in the transmission of electrical impulses through the heart. As a result, the heart does not pump the blood properly, and it may pool and clot. If a blood clot forms and moves to an artery in the brain, atrial fibrillation can lead to stroke.
The major risk factors for atrial fibrillation include age, coronary artery disease, rheumatic heart disease, hypertension, diabetes, and thyrotoxicosis. Atrial fibrillation affects 7% of the population over 65 years of age, and is also associated with increased risks of congestive heart failure and cardiomyopathy, which warrant medical attention and treatment. Atrial fibrillation is the most common sustained heart rhythm disorder and increases the risk for heart disease and stroke, both leading causes of death in the United States.
To treat cardiac arrhythmias including atrial fibrillation, physicians often employ specialized ablation catheters to gain access into interior regions of the body. Such catheters often include tip electrodes or other ablating elements used to create ablation lesions that physiologically alter the ablated tissue without removal thereof, and thereby disrupt or block electrical pathways through the targeted tissue.
In the treatment of cardiac arrhythmias, a specific area of cardiac tissue having aberrant electrically conductive pathways, such as atrial rotors, emitting or conducting erratic electrical impulses, may be initially localized. A physician may direct a catheter through a main vein or artery into the interior region of the heart that is to be treated. The ablating portion of the selected device is next placed near the targeted cardiac tissue that is to be ablated, such as a pulmonary vein ostium or atrium.
An ablation procedure may involve creating a series of inter-connecting lesions, to electrically isolate tissue believed to be the source of an arrhythmia. During such a procedure, a physician may employ several different catheters having variations in geometry and dimensions of the ablative element in order to produce the desired ablation pattern. Multiple devices having varying dimensions and shapes may also be used, to account for variations in anatomy. Each catheter may have a unique geometry for creating a specific lesion pattern or size, with the multiple catheters being sequentially removed and replaced to create the desired multiple lesions.
For example, some catheters may be capable of following a two-dimensional curve, which may be referred to as “curvilinear” or “linear” ablation. Other catheters may be capable of forming a three-dimensional shape, such as a loop that is almost transverse to the catheter's longitudinal axis, which may be referred to as “loop” ablation.
Accordingly, it is desirable to provide a single medical device capable of both linear and loop ablation, thereby reducing the need for additional medical devices.